Superelasticity and the propagation of shock waves in crystals

Abstract

The invention of lasers capable of generating fem� tosecond pulses opens a way for investigating fast pro� cesses in matter. The development of the diagnostic methods for the subpicosecond timescale was of exceptional importance. With these methods, not only the generation, but also the measurement of fast pro� cesses initiated by a femtosecond laser became possi� ble. The initiation and measurements are performed with a pair of ultrashort pulses using the stroboscope principle [1–7]. The first pulse in the pair is a high� power pump pulse and the second pulse is a weak probe pulse (pump–probe method). Both pulses are formed by means of the separation of a single initial pulse. They pass through paths with different optical lengths and arrive at a target at different times. The time delay t delay of the arrival of the probe pulse with respect to the pump pulse is varied by the controlled variation of the optical length. Thus, a series of the phases and amplitudes of the probe pulse reflected from the place of the action of the pump pulse in t delay is obtained. The phases and amplitudes provide infor� mation on time variation of the optical characteristics and on the fast evolution of heated matter. The pump pulses and the places of the irradiation of the target should be the same in different experiments of the series for success of the pump–probe method.